This invention relates to the dissipation of static electricity in specialised workwear and more particularly to antistatic workwear, that is clothing or other garments worn for work.
As electronic components become smaller and more sensitive they may be easily damaged by static electrical charges. It is therefore important that operatives engaged in the manufacture of such components are at earth potential, that is they do not carry a static electrical charge. For this purpose specialised workwear, for use in the micro electronics industry, has been developed made from tightly woven fabric incorporating a grid or stripe of electrically conductive yarn. This is designed to dissipate static electrical charges which would otherwise build-up as the article of workwear is worn. In particularly sensitive situations static dissipation is improved by earthing the operator, the workwear or both.
As well as in the microelectronics industry, the control of static build-up in workwear is also important in the pharmaceutical and microbiological industries, for three main reasons. Firstly, the build up of an electrostatic charge may cause attraction or repulsion of bacteria or microscopic particles of active pharmaceutical agents, thereby changing the performance of the protective workwear, which may not only serve to protect the product from contamination but also protect the wearer from contact with the materials being handled. The performance of the workwear is therefore closely specified, and the effects of electrostatic attraction or repulsion of materials may be that the performance standard is not achieved in practice. By reducing the electrostatic charge to zero or a very low voltage consistently, the performance of the workwear can be guaranteed. Secondly, the build-up of electrostatic charge can involve arisk of discharge to neighbouring earthed surfaces, giving rise to sparks which can ignite flammable vapours used in processing, for example. The third reason is allied to the second, in that the discharge of high electrostatic voltages through sensitive electronic measuring or monitoring equipment can lead to false readings or to damage. In the context of medical work, false readings or disruption to monitoring equipment could have very serious consequences for patients, for example.
Difficulties can arise in relation to such workwear due to the fact that the conductive filaments are woven into the fabric and as such come to the surface of the fabric relatively infrequently and in an erratic manner. As a result if one piece of fabric is placed on top of another, as occurs, for example in the case of a seam between adjacent parts of an article of workwear, the electrically conductive filaments in each piece of fabric are unlikely to make contact or satisfactory contact with one another with the result that it is unlikely a satisfactory electrical connection will be made across the seam. A similar problem arises in the case of an article of workwear consisting of more than one garment, for example where a hood or an item of footwear are used in association with a main garment. As a result it is difficult to earth all of the garments from a single earthing point.
In U.S. Pat. No. 5,715,536 there is disclosed a static electricity dissipating garment in which a continuous conducting ribbon extends through all the seams and is connected to a grounding wire. Similarly, in U.S. Pat. No. 4,546,497 there is disclosed antistatic clothing incorporating electroconductive tape in the seams. U.S. Pat. No. 4,606,968 discloses a base fabric, for use in antistatic garments, having an integrally woven or knitted grid structure which is raised above the surface of the base fabric to provide increased electrostatic dissipation performance, the grid being formed from a static discharge yarn plied to a carrier yarn which is then woven or knitted into the fabric in the warp direction.
It is therefore known for antistatic workwear to comprise a plurality of components incorporating electrically conductive yarns and an electrically conductive member bridging the junction between adjacent components.
A problem which arises with antistatic workwear is that the antistatic properties tend to degrade with repeated cleaning. For example, workwear may be washed, chemically treated (so-called xe2x80x9cdry cleaningxe2x80x9d) and/or radiation treated to ensure that it is clean and sterile. It has been found that the residual static voltage on the workwear tends to rise with repeated cleaning cycles until it reaches an unacceptable level. For conventional workwear of the types described, it has been found that this state is reached long before the workwear has otherwise come to the end of its working life.
According to the present invention an article of workwear comprises plurality of components incorporating first electrically conductive yarns, and an electrically conductive member bridging the junction between adjacent components, wherein the electrical conductivity between adjacent components is enhanced by forming the electrically conductive member from a strip or tape incorporating plurality of second electrically conductive yarns which are of larger diameter than said first electrically conductive yarns, portions of the second electrically conductive yarns are exposed along the length of the strip or tape alternately on a first side and a second side of the strip or tape, and the component and conductive member are attached to one another such that the second electrically conductive yarns are in electrically conducting engagement with at least some of the first electrically conductive yarns in both adjacent components, the first electrically conductive yarns are more widely spaced than the second electrically conductive yarns are sharply bent by the structure of the strip or tape to promote a corona discharge.
Throughout the specification and the claims the word xe2x80x9cyarnxe2x80x9d is used generically to any yarn, fibre, filament or equivalent component of a workwear fabric, strip or tape. At least some of the electrically conductive yarns may be formed from a carbon-coated polyamide or a conductive polyester.
The first electrically conductive yarns in the components preferably have a diameter of between 0.01-0.05 mm, and the second electrically conductive yarns in the strip or tape a diameter of between 0.5-1.0 mm.
The strip or tape is preferably stitched to each of the adjacent components. However, it will be understood that other methods of attachment may be used, for example welding using heat, ultrasonics or high frequency electromagnetic radiation, or adhesives.
Preferably, each component is of woven construction.
The term xe2x80x9ccomponentxe2x80x9d is used herein to refer both to adjacent components of a single article of workwear and adjacent garments or other items which together form a complete article of workwear. A single article of workwear may, for example, be formed from a number of panels connected together by seams, each of the panels comprising a component of the complete article of workwear. Alternatively an item of workwear may consist of a number of separate articles which are worn together such as a body garment, a hood and articles of footwear, each of which comprises a component of the overall article of workwear.
Where the article of workwear comprises a single garment, the components may comprise adjacent panels from which the garment is constructed and which are connected to one another by seams. In such cases the strip or tape may extend transversely across each seam formed between adjacent components of the article so as to bridge the seam and interconnect electrically conductive members incorporated in the respective panels. Alternatively the strip or tape may be incorporated longitudinally into a seam formed between adjacent components whereby the strip or tape will be in surface contact with each of the panels connected together at the seam.
Where the components comprise a plurality of separate garments employed together to form a complete article of workwear, the strip or tape may incorporate fastening means for interconnecting the separate garments, such fastening means being adapted for engagement with complimentary fastening means on an adjacent article, the respective fastening means being associated with respective strips or tapes bridging a plurality of conductive fibres incorporated in each of the articles to provide electrical continuity. The articles may comprise an upper body or jacket portion of a garment and a lower body or trouser portion. Alternatively, or in addition, the articles may comprise a hood together with an upper body portion or a unitary upper and lower body portion of a garment. In either case the lower body portion of the garment may incorporate integral or separate articles of footwear.
Alternatively, the articles may comprise a complete body garment or a lower body garment and associated articles of footwear, said electrically conductive member extending across the junction of one articles to the other and being connected to or juxtaposed with one or both of the articles.
Alternatively, an electrically conductive member may be associated with each article, the electrically conductive members incorporating complementary fastening members adapted for engagement with one another to secure the articles together and form an electrically conducting path between them. The complementary fastening members may comprise components of a press or stud fastener.
in an alternative arrangement the workwear may comprise an electrically conductive stirrup, opposite ends of which are secured to lower edge regions of leg portions of a garment, the stirrup being adapted to extend beneath the wearer""s foot in contact with an article of footwear having an electrically conductive sole. The stirrup member may be located around the wearer""s foot internally of the article of footwear whereby to be compressed in use between the wearer""s foot and the inner surface of the conductive sole of the article of footwear.
Alternatively, the stirrup member may be arranged to extend around the outer surface of an article of footwear whereby to be compressed in use between the outer surface of the conductive sole of the article of footwear and the floor.
Each strip or tape incorporates a plurality of electrically conductive yarns which may comprise filaments formed from or coated with electrically conductive material. The strip or tape may advantageously be formed from woven polyester fabric incorporating electrically conductive yarns. In a typical construction the electrically conducting yarns in the strip or tape from which the articles are constructed are arranged to form a 5 mm grid pattern, the electrically conducting fibres in the electrically conducting member being arranged in parallel lines approximately 2 mm apart.
It is believed that the use of a strip or tape with conductive elements woven into it in such a way as to protrude from the surface of the strip or tape helps to enhance electrical conductivity in two ways:
1. The protrusions are forced into the fabric of the seam by virtue of the stitching, ensuring physical contact between the electrically conductive elements in the strip or tape and those in the fabric of the component; and
2. The protrusions formed by the sharply bent conductive yarns may promote corona discharge at above about 500 volts, so increasing the rapid conduction of charge across the seams. It is thought that this corona discharge is responsible for the extremely rapid and successful discharge from the made up antistatic workwear.
In addition, antistatic workwear in accordance with the invention has been found to retain its ability to dissipate electrostatic charge after repeated cleaning and sterilisation treatment. For example, workwear subjected to 60 typical wash and wear cycles has shown no significant change in the ability to dissipate charge, and equally workwear subjected to 60 gamma radiation sterilisation cycles also displayed no loss of electrical bonding in the seams. Workwear in accordance with the invention is therefore considerably more economical in use, lasting many more cycles of use and cleaning/sterilisation than conventional antistatic workwear.